In certain, non-limiting embodiments, cable communication systems such as those defined by Data Over Cable Service Interface Specification (DOCSIS) 3.1 FDX, although the inventive embodiments are not limited to any specific defined protocols. DOCSIS 3.1 FDX specifications impose additional challenges on the filtering design of that did not exist in prior versions of the standard.
DOCSIS 3.1 FDX allows dynamic resource block allocation (RBA) for downstream and upstream in the FDX band. Meaning that a channel that is receiving may be changed and allocated to transmission and vice versa. In order to cope with the changed electrical characteristics due to the filter switching for RBA changes, it may be desirable to change the digital compensation for the channel response (i.e., adjust equalizer coefficients) according to the changes in the filter configuration.
By way of example only, consider a rudimentary case of a system that uses three resource block allocations (RBAs), such as when two RBAs, also referred to herein as “channels,” are allocated to downstream and one RBA to the upstream. If, for example, the network changes the resource block allocation of the cable modem tuner to one downstream channel and two upstream channels, i.e., one of the downstream channel allocations is changed to an upstream channel, the filtering at the receiver will change, as well as does the likely need to adjust the equalizer coefficients to match electrical changes due to an alternate filter input. As the downstream is frequently receiving most of the time, the filter switching due to a resource allocation change will likely happen while the CM is receiving real data. Due to filter design and matching, the impedance and the frequency response that is seen at the tuner input, after filtering, will change with RBA changes. This may cause errors in signal demodulation as the change may affect the amplitude and phase of the signal at the analog to digital controller (ADC) input if no compensations for these changes are made at the same time, or nearly simultaneously, in time.
If the update of equalization coefficients is not well timed to match the filter switch, then there very likely will be a period of time when inefficient or incorrect equalizer coefficients are used and thus degrade performance of the receiver in receiving the downlink channel, including possible data loss. It would therefore be desirable to have a method/process and/or architecture to provide synchronization of filter switching and equalizer coefficient updates due to changes in RBAs, which may be necessary in DOCSIS 3.1 FDX operation or similar uplink/downlink communication systems using FDX filter switching.